Reactive diafiltration for assembly and formulation of virus-like particles

An emerging paradigm to quickly and cost-effectively manufacture virus-like particle (VLP) biopharmaceuticals involves VLP subunit production in highly productive bacterial hosts, followed by assembly in a controlled cell-free environment. Study of cell-free VLP assembly has yet to progress beyond laboratory-based dialysis methods, which are slow and buffer intensive, and are thus difficult to scale. In this study, a scalable cell-free VLP assembly and formulation process using a single diafiltration unit was developed. A reactive constant volume diafiltration VLP assembly process was systematically and quantitatively designed to maximize VLP yield. Using a dilute concentration of capsomeres during VLP assembly minimized membrane-induced aggregation. Optimizing the assembly buffer exchange rate, and the rapid introduction of calcium ions to the assembly mix, facilitated the propitious assembly of VLPs. An absolute increase in VLP yield of 42–56%, compared to initial laboratory-scale batch diafiltration assembly processes, was achieved. The optimized process produced high-quality VLPs (PDI = 1.08 ± 0.01) at high yield (78%). The constant volume diafiltration method has the added advantage of being scalable and represents a high level of process intensification. The methodology reported in this study, based on quantitative analysis of the influences of process changes, is consistent with modern engineering approaches, and can ultimately lead to cheaper and quicker VLP manufacturing routes and hence the accelerated translation of products from laboratory settings.

► Rate of assembly buffer exchange dramatically affects VLP yield and quality.
► VLP assembly diafiltration reactor designed with optimized buffer exchange rate.
► Integration of assembly and formulation in a single diafiltration unit demonstrated.
► Diafiltration assembly and formulation gave high final VLP yield of 53%.
► Intensified VLP process via reduced process units and buffer consumption.